This application relates generally to inspecting objects, and more specifically to methods and apparatus for inspecting objects using a light measurement system.
Objects are sometimes inspected, for example, to determine a size and/or shape of all or a portion of the object and/or to detect defects in the object. For example, some gas turbine engine components, such as turbine or compressor blades, are inspected to detect fatigue cracks that may be caused by vibratory, mechanical, and/or thermal stresses induced to the engine. Moreover, and for example, some gas turbine engine blades are inspected for deformations such as platform orientation, contour cross-section, bow and twist along a stacking axis, thickness, and/or chord length at given cross-sections. Over time, continued operation of the object with one or more defects may reduce performance of the object and/or lead to object failures, for example, as cracks propagate through the object. Accordingly, detecting defects of the object as early as possible may facilitate increasing the performance of the object and/or reducing object failures.
To facilitate inspecting objects, at least some objects are inspected using a light measurement system that projects a structured light pattern onto a surface of the object. The light measurement system images the structured light pattern reflected from the surface of the object and then analyzes the deformation of the reflected light pattern to calculate the surface features of the object. More specifically, during operation, the object to be inspected is typically coupled to a test fixture and is then positioned proximate to the light measurement system. A light source is then activated such that emitted light illuminates the object to be inspected. However, because the light source also illuminates at least a portion of the test fixture, and/or portions of the object outside an area to be inspected, a resultant image of the object may include noise caused by inter-reflections between the object and portions of the test fixture illuminated by the light source, and/or between an area of the object to be inspected and portions of the object outside the area to be inspected. For example, such inter-reflections may be caused if the test fixture has a shape or finish that casts reflections on the object, and/or if the object has a relatively mirror-like finish that reflects an image of the test fixture. Moreover, ambient light may also cause noise in the resultant image. Noise caused by such inter-reflections and/or ambient light may result in reduced image quality and poor measurement results, possibly leading to an incorrect interpretation of surface features of the object.
Accordingly, at least some known light measurement systems include a physical mask that is formed, for example, from a sheet of paper or metal. The physical mask limits an area illuminated by the light source to facilitate reducing inter-reflections between the test fixture and the object. However, because such physical masks are uniquely formed for the geometry and/or orientation of a particular object, such masks generally are not interchangeable and need to be changed when the object is re-orientated or when a different object is inspected. Moreover, fabrication of such physical masks may be time-consuming.